23. Tracleer is a drug for high blood pressure (generic name bosentan).

24. Trantor is a planet in the Foundation series of books by Isaac Asimov.

25. Trelstar is a treatment for prostate cancer (generic name triptorelin).

26. Valeron is a river in the Darkover series of books by Marion Zimmer Bradley.

27. Zorac is Time Lord in Dr. Who… but also a psoriasis medication (it's the British brand name of Tazorac, generic name tazarotene). Tricked again!

Why was that so hard? (Which it surely was unless you're a hardcore sci-fi/fantasy geek or a licensed pharmacist.) Why are they all so similar?

To be fair, there's also a selection effect: I picked ones that would be hard to guess. There are plenty of sci-fi and fantasy names that don't sound like drug names—in fact, fantasy novels often like the Celtic flavor, with lots of double l's and th's and so on, and sci-fi characters often have names pretty much like normal human names. There are also drug names that are more obviously drug names—and ones you see more often, like Prozac, that would be slam-dunks.

But what the names above have in common is that they are written to be catchy, or to have an exotic flavor. The least common letters in normal English usage are V, K, X, J, Q, and Z, and the least common vowel (when it's used as one) is Y. So words that use those tend to stand out more, and you can see how common those uncommon letters are in these names. On the other hand, many names that are thought to be attractive end in a, so that gets used quite a bit too. Drug names also are more likely than ordinary words to end in on or l or c for historical reasons.

But they still all conform to our expectations of what a word should be like. All of the names have sequences of consonants and vowels that are allowable in English (well, except Qvar, but we can still pronounce it). There's no Rfova or Ejxade. Most of them are two syllables, and they tend to have one syllable that is clearly heavier—it has a long vowel or two consonants following the vowel—so the pronunciation is clear. They may be exotic, but they're familiarly exotic.

They also may have familiar sounds—some drug names remind you in some way of the disease they're treating or the solution they offer to the problem (think or Rogaine for hair loss), and sci-fi and fantasy names may have a bit of an echo of some familiar name that they can draw some force from. Just as long as they're still catchy.

And one more thing: They're all made up by nerds—sci-fi/fantasy writers or drug company wonks. And anyway, with drug companies named things like Glaxo and Shire, what do you expect?

*Correction, Jan. 21, 2014: A previous version of this post stated that Exjade is a treatment for osteoarthritis. It is in fact a treatment for too much iron in the blood.